Numerous lines of evidence suggest that the extended medial amygdala (MeA) mediates both approach and avoidance aspects of behavior. However, specific neuronal populations have not previously been identified that respond selectively to social stimuli that are of a positive or negative valence. The identification and investigation of valence-sensitive amygdalar neurons would provide novel information about normative regulation of approach-avoidance behavior and sociality, and would generate important insights into mechanisms that may underlie social anxiety and clinically-relevant deficits in social behavior. During the initial funding period for this grant, we established a research program to examine neural mechanisms of sociality, using five finch species that differ strongly in their species-typical group sizes (the species are territorial, modestly gregarious, or highly colonial), but not in other important ways (e.g., all of the species are monogamous). This system is providing numerous insights into the mechanisms of sociality, and we have now clearly established that valence sensitivity (selectiveness for positive stimuli) is exhibited by vasotocin- immunoreactive (VT-ir) neurons in the medial bed nucleus of the stria terminalis (BSTm;a component of the extended MeA). Response profiles of these neurons also differ in relation to species-typical group size, such that same-sex conspecific stimuli elicit stronger responses in gregarious species than in territorial species. Homologous neurons are found in virtually all land vertebrates, including humans. The experiments proposed here will further elucidate functional properties of valence-sensitive VT neurons, and will seek to identify and characterize BSTm neurons hypothesized to exhibit a sensitivity to negative valence. We will also address the general hypotheses that 1) dopamine (DA) inputs influence socially-elicited responses of VT neurons, and 2) DA and VT interact to regulate approach-avoidance. As with VT, DA is known to influence a wide range of social behaviors, and DA plays a major role in generating positive affective states. We will employ a diversity of approaches, including the use of DA lesions, administrations of agonists and antagonists, extensive behavioral assessments, and analyses of Fos induction (inclusive of multi-labeling with VT and TH). We additionally propose the development of VT RNA interference that will enable us to specifically knock down VT production, thus allowing the functional investigation of specific VT cell groups.